The present invention relates to an arc discharge path for the generation of shock waves to be focused for non-invasive comminution of concrements in the body of a living being, whereby an arc is preferably produced under water, i.e. in a liquid coupling medium, and in-between two electrodes.
German patent 23 51 247, corresponding to U.S. Pat. No. 3,942,531, suggests a device for generating and focusing shock waves and generally describes procedures for the comminution of concrements, such as kidney stones without invasive surgery, the concrements being, of course, in the body of a living being. For a general discussion see, for example, Chaussy (ed) Extracorporeal Shock Wave Lithotripsy, Karger, 1982. Known and practiced devices of long successful standing include a focusing chamber being constructed as a partial rotational ellipsoid; a spark gap is provided for the production of an arc in one of the two focal points of such an ellipsoid; the other focal point is located in the concrement to be comminuted by focused shock waves. The shock waves, particularly as produced by arc discharge in the first one of the focal points propagates in all directions, and is reflected by the rotational ellipsoid and focused into the second focal point. The arc is preferably produced in a spark gap between two electrodes and upon discharge of an electrical capacitor so that a definite amount of electrical energy is converted into mechanical, shock wave energy. As the arc is fired in a very limited region, the rotational ellipsoid reflection permits a near point-like focusing of the shock wave with amplitudes being added to reach peaks in excess of 1 kbar, and for pulse durations below a micro second. Highly concentrated, strong, mechanical forces are, thus, concentrated in the concrement and readily destroy it resulting in a large number of small granules and fracture pieces which can be discharged from the body of the living being by natural processs.
German patent 26 35 636 discloses in greater detail electrodes of the type to which the invention pertains and for the particular purpose invisioned here; see also U.S. Pat. No. 4,608,983 of common assignee. A holder is provided and the electrodes project from that holder. One of the electrodes, so to speak, extends in a cage-like fashion over and beyond the particular focal point and doubles back in form of a loop, while the other electrode is directly oriented to face that point towards which the first mentioned electrode is doubled back, so that together and by means of their tips, they form a very small gap. These electrodes will face each other along an axis. One of the electrodes is, as stated, preferably constructed as a cage which carries a sleeve with a bore for fastening the electrode tip as a separate element. The cage maybe formed from two or more arc-shaped loops or the like. The other electrode just has a sleeve with a tip element in straight aligned fashion.